Where are substituted BAD values coming from?

We are experiencing a problem where good data is being substituted by Bad values.

I know the snapshot value was good, because the analysis using the data is done correctly. But after some time the data gets substituted and the analyses will fail when using the backfill/recalculating option.

The data itself is collected by the PI Connector for OPCUA. The tags I'm referring to are of datatype String. Seems other data types doesn't have this problem.

Any idea which application is responsible for the substituted bad value? Why and how to prevent?

Could you please check the OPC UA using client and check if you are having any bad data for that particular timestamp? AF analysis generally writes "Calc Failed" if case of any issues with calculation or report error. Would like know if there is any problem with input tags.

You would want to make sure that the data really is being written by the same connector instance. You can first review the Network Manager statistics to see if you do not have a second instance of the OPC UA connector running, where you are not aware. Additionally, if using PI Data Archive 2017+, you can leverage the Snapshot_TracePointID tuning parameter.

2-OPC UA configuration

Would you be able to share the configuration of one of your problematic string tags? For example:

Also, please let us know if you are using any custom values in the App.OpcUa.Config, as it can change the client stack layer interaction with the OPC UA Server.